Applications of Architectural Acoustics Tufts University – ES65 September 07, 2017

Outline Sound Proofing vs. Acoustical Treatment Concerns addressed through acoustical treatment Materials used in acoustical treatment Measurement tools in acoustic analysis Considerations in small recording spaces Next steps

Sound Proofing Reducing sound transmission between spaces Source: Dan Russell, Penn State Mass = A+ sound proofing Air Between Two Decoupled Walls = B sound proofing Click 1 – Animation Click 2 – Wall Added Click 3 – Wall + Air added Click 4 – Mass & Air

Sound Proofing Achieved with: Mass, Isolated Construction and Tight Closures Cinder blocks for speaker stands, heavy doors Room-within-a-room construction Door, window and wall seals See White: Chapter 18 for more information

Acoustical Treatment Designed for correction http://www.respace-acoustics.co.uk/files/9312/8206/0734/Acoustic_WallPanel_C_Ecophon.jpg

Acoustical Treatment Designed for a particular purpose and character

Acoustical Treatment Designed for recording instruments & ensembles

Acoustical Treatment Designed for critical listening and assessment

Reflections V λ= f Hard flat surfaces will reflect sound like a mirror Any hard flat surface that is larger than the wavelength of a particular frequency will likely reflect energy at that frequency and above Frequency 1 kHz Wavelength 1 foot λ= V f Period 1 ms FLUTTER ECHOS FOCUSES Wavelength = Period / Frequency??? (look this up)

Reflections Echoes are distinct reflections where we can pick out the individual occurrences. We start hearing distinct delays around 20 ms Reflections of less than 20 ms can result in comb filtering Comb filter caused by two signals generated1 ms apart Flutter echos are a concern for small rooms and studios.  These occur when high-frequencies are reflected multiple times.   Reflections of less that 20 ms can result in comb filtering Desks Play examples of a microphone on a desk stand Music stands Have them speak into a music stand, then add foam Hard surfaces around speakers Take a portable studio monitor, set it up in a corner, then move it away Control room glass http://www.moultonlabs.com/images/gallery_images/articles/about_comb_filtering7.gif http://www.moultonlabs.com/more/about_comb_filtering_phase_shift_and_polarity_reversal/

Frequency Specific Issues Modes or Standing Waves Can be calculated and mitigated Types of room modes: Axial = 2 surfaces Tangential = 3 surfaces Oblique = 4 or more surfaces http://fmarvasti.com/Graphics/ModeTypes.jpg

Calculating Axial Modes Speed of Sound (1130 ft/second) Dimension between the two boundary surfaces Frequency of the mode f = n(c / 2D) Positive Integer LENGTH WIDTH HEIGHT 1st Mode 2nd Mode 3rd Mode 4th Mode

Frequency Specific Issues Nodes Hard to prevent; move your groove thing

Treatment Materials Absorbers Diffusors Reflectors

Absorbers Convert acoustical energy into heat Common absorbers Foam The amount of heat generated is marginal Common absorbers Foam Carpet Draperies Soft furniture Large Mammals Absorbers attenuate sound

Absorption Coefficients Measured across the spectrum 0 = perfect reflector 1 = perfect absorber Noise Reduction Coefficient = average of four octaves (250, 500, 1k, 2k) We generally want to absorb equally across the spectrum White pg. 169 has coefficients for common materials

Decay time

Calculating decay time Sabine’s Equation: V = volume of the space (in cubic feet or meters) S = absorbing surface area (in ft2or m2) A = absorption coefficient (in Sabins) 0.049Vf SA RT60 = 0.161Vm SA RT60 = http://www.accutronicsreverb.com/design/default/images/sub_05/rt60chrt.jpg This would have to be totaled for different absorption coefficients at different frequencies, and different absorptive materials throughout a space. You can imagine how insane that could get with a space like Distler… There are more expansive versions of this formula to address further complexities of actual spaces. This is only a very rough estimate.

Measuring decay time http://www.accutronicsreverb.com/design/default/images/sub_05/rt60chrt.jpg http://www.sengpielaudio.com/RT60-01.gif

Anechoic Spaces Used for measurement Measurement of sound, antennas, vibration. Equal absorption across the spectrum Also radically low noise floor Some people claim they cause hallucinations Because they absorb so much energy, and require a great deal of energy to move air molecules inside of them http://aragec.com/anechoic+chamber.html

Diffusors Blackbird Studio, Nashville Diffusion SCATTERs sound

Diffusors Quadratic Fractal Quadratic, Fractal, phase grating, formulas depend on what part of the spectrum you aim to diffuse.  Free construction plans at http://arqen.com/ Book cases and interrupted walls without large parallel surfaces help Frequency and scatter patterns depend on size/shape

Reflectors Parallel Walls Offset/non-parallel designed walls to redirect sound Domes & curves

Intentional Reflectors Acoustic shells Kennedy Center – before & after acoustic shell

Measurement tools EASE SMAART REW Faber Acoustical

Building a small studio Recording or critical listening/voice?

Speaker placement Use heavy cinder block speaker stands to decouple from the floor 6 ft.

Mix Position 6 ft. Node? Especially in the center of a room Area of optimal reflections Too few reflections from the side can affect imaging

Major reflection issues B O K S Beware of desk reflections 6 ft. RACK OF CLOTHES B O K S Grow more hair Flutter echoes Will make you crazy Modes Could just be an awareness or EQ correction

Isolation & sound proofing What sounds don’t we want in the recording space? What sounds don’t we want in the control room? Computer noise Refrigerators Cell phones Cats All of the above Transferred energy from the recording space(s)

Recording Acoustic Instruments Special Concerns Sound proofing Room volume Does the sound have time to develop? Ambient noise floor HVAC Computers and noisy devices Sonic character

Safety and Aesthetics Fireproofing is a thing Aesthetics are also a thing If it sounds good, is it good?

Work with what you have Check low-end in good quality headphones Look for drastic gestures in your work Just do something and learn

Next Steps Fields of acoustics Architectural Acoustics Graduate Programs Internships related to Architectural and Musical Acoustics Job descriptions for careers related to Acoustics Play with free toys, check out additional resources What can you do to optimize your own space?